1. Field of the Invention
The present invention relates to a valve moving apparatus of an internal combustion engine having a mechanism for changing valve operating characteristic such as lift amount of at least one of an intake valve and an exhaust valve of the internal combustion engine in accordance with operating condition of the engine.
2. Description of the Related Art
Hitherto, as an apparatus for changing valve operating characteristic such as lift amount of an intake valve or an exhaust valve of an internal combustion engine in accordance with operating condition of the engine, a valve timing control apparatus of an engine disclosed in Japanese Laid-Open Patent Publication Hei 6-117207 has been known, for example. This apparatus comprises a rocking cam for opening and closing an intake valve or an exhaust valve, a driving cam for rocking the rocking cam supported on a camshaft rotated by power from a crankshaft, and a valve timing variable mechanism provided at one end of the camshaft for moving the camshaft axially and changing rotational phase of the camshaft with respect to the crankshaft. The driving cam is formed in a shape tapered in direction of axis of the camshaft.
When the camshaft is moved in one axial direction by the valve timing variable mechanism in accordance with engine operating condition, the valve is opened with a smaller lift amount and a smaller operation angle by the rocking cam rocked by the tapered driving cam which moves axially together with the camshaft. On the other hand, when the camshaft is moved in another direction, the valve is opened with a larger lift amount and a larger operation angle. Further, when the camshaft and the driving cam move axially, rotational phase of the camshaft with respect to the crankshaft is changed, and therefore a crank angle at which lift amount of the valve becomes maximum is also adjusted.
In the above prior art, since the driving cam for changing lift amount and operation angle of the valve is moved in a body with the camshaft by the valve timing variable mechanism, weight of an object to be moved by the valve timing variable mechanism (driving cam) is large, and further, sliding resistance of the camshaft supported by an engine main body is added. Therefore, response to change of the valve lift characteristic is not good. If a large driving force is desired in order to improve the response, the valve timing variable mechanism and the engine become large.
The present invention is achieved in view of the foregoing, and an object of the present invention is to provide a valve moving apparatus of an internal combustion engine that response to change of valve operating characteristic of an intake valve or an exhaust valve can be improved and the internal combustion engine can be miniaturized.
The present invention provides a valve moving apparatus of an internal combustion engine having an intake camshaft provided with at least one intake cam piece for opening and closing an intake valve, and an exhaust camshaft provided with at least one exhaust cam piece for opening and closing an exhaust valve, at least one of the intake cam piece and the exhaust cam piece being a variable cam piece provided with a variable cam section having different valve operating characteristics changing in direction of a rotary axis of the intake camshaft or the exhaust camshaft for opening and closing:the intake valve or the exhaust valve in accordance with the valve operating characteristic including lift amount and operation angle, wherein: the variable cam piece is provided on the intake camshaft or the exhaust camshaft so as to slide in direction of the rotary axis; a driving mechanism for moving the variable cam piece in direction of the rotary axis in accordance with engine operating condition to change the valve operating characteristic of the intake valve or the exhaust valve is provided; the driving mechanism comprises a movable member driven so as to reciprocate along a center axis, and arms extending from the movable member toward the intake camshaft or the exhaust camshaft having contact sections contacted with both side surfaces of the variable cam piece in direction of the rotary axis, respectively; and the center axis of the movable member is positioned near a center line of a cylinder of the internal combustion engine more than the rotary axis of the intake camshaft or the exhaust camshaft.
According to the invention, when the variable cam piece is moved in direction of the rotary axis of the camshaft to change valve operating characteristic of the intake valve or the exhaust valve, the driving mechanism moves the variable cam piece, which is provided on the camshaft so as to slide, in direction of the rotary axis of the camshaft, so that the movable cam section having different valve operating characteristics changing in direction of the rotary axis opens and closes the intake valve or the exhaust valve. Weight of the variable cam piece moved by the driving mechanism is very small compared with total weight of the driving cam and the camshaft of the above-mentioned prior art, therefore, a large driving force is unnecessary and the driving mechanism can be miniaturized.
Since the driving mechanism moves the variable cam piece of light weight when the valve operating characteristic of the intake valve or the exhaust valve is changed, the movement in direction of the rotary axis is carried out rapidly and response to change of the valve operating characteristic is improved, so that operation region that the engine is operated with a most suitable valve operating characteristic is widened and engine performance such as engine output can be improved. Further, since the driving mechanism can be miniaturized, the valve moving apparatus can be miniaturized and therefore the internal combustion engine can be miniaturized.
Since the movable member is positioned near a center of the cylinder more than the intake camshaft and the exhaust camshaft, and the contact section touching the variable cam piece to give driving force of the movable member to the variable cam piece is provided on the arm extending from the movable member toward the intake camshaft or the exhaust camshaft, the driving mechanism can be put within a width of the camshaft in direction of straight line perpendicular to the rotary axis of the camshaft. Therefore, a width of the valve moving apparatus in direction of the straight line does not become large. Further, since the contact sections touchxc3xa9 the respective side surfaces of the variable cam piece, the contact sections does not influence rotation of the variable cam piece which rotates together with the intake camshaft and the exhaust camshaft.
As the result, the drive mechanism is disposed between the intake camshaft and the exhaust camshaft, width of the valve moving apparatus in direction of the straight line perpendicular to the rotary axis of the both camshafts does not become large, the valve moving apparatus can be miniaturized and the internal combustion engine can be miniaturized. Further, since the contact sections touch side surfaces of the variable cam piece so as not to influence rotation of the variable cam piece, the intake valve and the exhaust valve can be surely opened and closed by the variable cam piece.
Preferably, the driving mechanism comprises the movable member having a center axis parallel with the rotary axis and a pair of arms extending from the movable member toward the camshaft and having the contact sections, and the movable member has a recess for allowing passing of the rotating variable cam section.
According to this constitution, the movable member can be disposed further close by the camshaft, because of the recess provided on the movable member.
The movable member may have both ends supported by neighboring cam holders respectively. Since the movable member can be supported utilizing the neighboring cam holders, any other member for supporting the movable member is unnecessary. Therefore, number of parts can be reduced, the valve moving apparatus and the internal combustion engine can be miniaturized.
An intake or exhaust rocker arm may be provided between at least one of the intake cam piece and the exhaust cam piece and the intake valve or the exhaust valve to open and close the intake valve or the exhaust valve. The intake or exhaust rocker arm is pivoted on an intake or exhaust rocker shaft and the driving apparatus have an oil passage for applying oil pressure to both end portions of the movable member. The oil passage may be constituted so as to pass through an inner portion of the rocker shaft.
According to such a constitution, an oil passage structure in the valve moving apparatus is not complicated, and arrangement of elements of the valve moving apparatus is not restrained by provision of oil passages for the driving mechanism.
A valve lifter may be disposed between at least one of the intake cam piece and the exhaust cam piece and one of the intake valve and the exhaust valve to come into contact with the intake valve or the exhaust valve. The valve lifter may be provided with a cut portion for escape of the intake cam piece or the exhaust cam piece not coming into contact with the valve lifter.
A cam of the cam piece not coming into contact with the valve lifter, which is adjacent to another cam coming into sliding contact with the valve lifter, rotates passing through the cut portion of the valve lifter without interfering with the valve lifter. Therefore, in a cam piece having a plurality of cams with respective different cam profiles, at least a part of a cam adjacent to a cam coming into sliding contact with the valve lifter can be positioned within a width of the valve lifter in direction of the rotary axis of the camshaft, so that the width of the cam piece in direction of the rotary axis can be made small, and the valve moving apparatus and the internal combustion engine is made compact and light. Further, since size of the cam piece in direction of the rotary axis is small, even in case that a plurality of engine valves for intake and exhaust are provided, cams for these engine valves can be disposed within a limited range of bore diameter of the cylinder. In addition, it is easy to provide cams more than three on one cam piece.
The cut portion may be formed by an opening penetrating the valve lifter so as to connect the inner side with the outer side. Lubricating oil on the outside of the valve lifter flows into the inner side of the valve lifter through the opening forming the cut portion, so that a valve spring disposed in the valve lifter, a retainer and a sliding portion of the engine valve is lubricated easily. Since a part of the valve lifter is cut off for forming the opening, weight of the valve lifter is reduced.
Preferably, each of the intake cam piece and the exhaust cam piece has a first cam section and a second cam section arranged in series in direction of the rotary axis, each of the intake valve and the exhaust valve includes a first engine valve and a second engine valve provided for the same cylinder, the valve lifter includes a first valve lifter disposed between the first engine valve and the first cam section and a second valve lifter disposed between the second engine valve and the second cam section, and the driving mechanism selectively switches over the first cam section and the second cam section coming into sliding contact with the first valve lifter and the second valve lifter respectively.
According to this constitution, the first engine valve and the second engine valve for each cylinder are switched by the same switch means. Namely a common switch means can be used for two engine valves. Therefore, the valve moving apparatus can be made compact.
A valve lifter may be provided between one of the intake cam piece and the exhaust cam piece and the intake valve or the exhaust valve, and the valve lifter may have a cut portion for escape of the arm.
Even if the arm touches a side surface of the cam section at a position radially projected from the base circle portion of the cam, the arm does not come into contact with the valve lifter because the arm is positioned in the cut portion. Therefore, the arm can be positioned within a width of the valve lifter in direction of the rotary axis of the camshaft, so that width of the driving mechanism in direction of the rotary axis can be made small to make the valve moving apparatus and the engine compact and light. Further, since positional relation between the arm and the valve lifter is restrained little, degree of freedom of arrangement of the arm and accordingly degree of freedom of arrangement of the driving mechanism become large.
A valve lifter coming into sliding contact with one of the intake valve and the exhaust valve may be provided between one of the intake cam piece and the exhaust cam piece and the intake valve or the exhaust valve, and a trigger mechanism for setting a switching action beginning time of the driving mechanism when the intake valve or the exhaust valve is closed may be disposed under the intake camshaft or the exhaust camshaft.
Since the trigger mechanism is disposed utilizing a space formed under the camshaft, the valve moving apparatus with the trigger mechanism miniaturized and accordingly the valve moving chamber and the internal combustion engine are miniaturized.
Preferably, the trigger mechanism is disposed between the intake camshaft or the exhaust camshaft and the lifter. The valve moving apparatus can be further miniaturized.
Preferably, the trigger mechanism is disposed overlapping with the lifter in moving direction of the lifter and acts in accordance with movement of the lifter. The valve moving apparatus having the trigger mechanism can be miniaturized in direction of the rotary axis of the camshaft too.
The variable cam piece has cams adjacent to each other having respective base circle portions smoothly connected with each other.
Preferably, the cam section of the cam piece includes a first cam section and a second cam section arranged in series in direction of the rotary axis, the engine valve includes a first engine valve and a second engine valve provided for each cylinder, the lifter includes a first lifter disposed between the first engine valve and the first cam section and a second lifter disposed between the second engine valve and the second cam section, and the trigger mechanism is disposed between the first lifter and the second lifter in direction of the rotary axis. The valve moving apparatus having the trigger mechanism can be miniaturized in direction of the rotary axis.
A lifter holding member may be constituted by a member separated from a cylinder head of the internal combustion engine, and the trigger mechanism may be fixed to the lifter holding member by means of a fixing member for fixing the lifter holding member to the cylinder head. Number of parts and assembling man-hour can be reduced.